Bibliographic details of the publications numerically referred to in this specification are collected at the end of the description.
The subject specification contains nucleotide and amino acid sequence information prepared using the program FastSeq Version 4.0, presented herein after the bibliography. Each nucleotide or amino acid sequence is identified in the sequence listing by the numeric indicator <210>followed by the sequence identifier (e.g. <210>1, <210>2, etc). The length, type of sequence (DNA, protein (PRT), etc) and source organism for each nucleotide or amino acid sequence are indicated by information provided in the numeric indicator fields <211>, <212>and <213>, respectively. Nucleotide and amino acid sequences which are defined in the Sequence Listing by the information provided in numeric indicator field <400>followed by the sequence identifier (eg. <400>1, <400>2, etc), are referred to in the specification as (“SEQ ID NO:1”, SEQ ID NO:2, etc).
The increasing sophistication of recombinant DNA technology is greatly facilitating research and development in the medical and allied health fields. This is particularly the case in the development of recombinant cytokines and growth factors for use in the treatment of diabetes, acquired immunodeficency syndrome (AIDS) and a number of cancers.
However, despite this developing knowledge of cytokine and growth factor effector molecules, their full exploitation requires an understanding of the corresponding cellular receptors and the complex biochemical and physiological signalling pathways initiated following interaction with ligands or following other stimulation such as disease, receptor aggregation or trauma.
A number of soluble trophic factors have been shown to exhibit an effect on neural survival in vivo. Many of these factors act directly on the developing neuron within, or example, the dorsal root ganglia (DRG). One factor of particular importance is nerve growth factor (NGF) [1]. The p75 neurotrophin receptor (hereinafter referred to as “p75NTR”), which is capable of associating with trk growth factor receptors, facilitates high affinity NGF binding and survival signalling. Although NGF has been proposed as a potential therapeutic molecule to promote survival of neurons, NGF is a multifunctional molecule and its pleiotrophy may adversely effect a range of non-neural cells.
p75NTR is also multifunctional. It has now been shown that p75NTR is capable of acting as a death receptor. Elevated p75NTR expression results in increased cell death in vitro and in vivo [24]. Furthermore, down-regulation of p75NTR prevents neural death after growth-factor withdrawal or axotomy [5, 6]. Consistent with the dual functions of p75NTR, mice with deleted p75NTR genes have a dramatic reduction of NGF dependent neurons, such as dorsal root ganglia, but increased numbers of other neuron populations (sympathetic and basal forebrain neurons) suggesting lack of naturally occurring cell death [7, 8]. p75NTR is also implicated in mediating death of neural, oligodendrocytes and Schwann cells [8, 9].
p75NTR is a member of the tumor necrosis factor (TNF) receptor/Fas superfamily, showing homology not only to the extracellular ligand binding domain but also to a cytoplasmic motif known as the “death domain”, so termed because of the cytotoxic actions of proteins containing the domain [9].
There is an accumulating body of evidence which suggests that p75NTR is involved in mediating cell death in a variety of degenerative diseases. During adulthood, p75NTR expression is down-regulated in most brain areas but is rapidly induced in ischemia (stroke) and results in transient increased p75NTR expression and apoptosis, as do both peripheral and motor nerve lesions [10-12]. p75NTR is also up regulated in patients with MND [13], and in experimental allergic encephalomyelitis (a model of multiple sclerosis; [14]). Intriguingly, in the basal forebrain and hippocampus, areas involved in learning and memory, p75NTR is highly expressed in aged rodents and in Alzheimer's patients, where extensive neural death is occurring [15, 16]. These data suggest that p75NTR is involved not only in normal developmental cell death, but may mediate the cell death occurring after injury or in neurodegenerative disease.
In work leading up to the present invention, the inventors sought to elucidate the region on p75NTR which mediates death signalling. The inventors surprisingly determined that the death signal is not the cytoplasmic motif known as the death domain [9] but is a region adjacent the membrane domain on p75NTR. The identification of this region provides for an opportunity to modulate cell survival by antagonising the death signalling region or promoting apoptosis by providing cells with the genetic material to express the death signalling region adjacent, proximal or otherwise juxtaposed or associated with the membrane or to express the death signalling region in multimeric form.